Child abuse affects over 1 million children each year in the United States at an estimated annual direct and indirect cost exceeding $103.8 billion. Many cases of physical child abuse are missed initially because early signs of abuse, such as bruising, go unrecognized. This lack of recognition leads to errors in decision making which in turn leads to poor patient outcomes. When abuse is missed, repeat injury occurs in up to 80% of victims with mortality rates as high as 30%; these cases are all preventable. Bruising is one of the most common signs of physical child abuse and is missed as an early warning sign in up to 44% of fatal and near-fatal cases. Currently, no evidence-based guidelines exist to aid clinicians in decision-making for discriminating bruises caused by abusive vs. accidental trauma. However, evidence from several studies indicates that discriminating characteristics do exist. The predictive accuracy of these findings has not yet been determined or incorporated into a practical decision-making model, such as a clinical decision rule, for the acute care setting. Clinical decision rules are point-of-care decision tools that help improve accuracy in decision making and may therefore improve health outcomes for children and families. This study will provide the first practical screening tool in the form of a bruising clinical decision rule (BCDR) for discriminating bruises caused by physical child abuse. The proposed study is a prospective observational study of bruising characteristics in children < 4 years of age. This proposal will build on previous work by the investigators in which a BCDR was derived for discriminating bruises caused by physical child abuse with excellent sensitivity (97%) and specificity (84%). Data on bruising characteristics will be collected by a pediatric emergency medicine research team and child abuse experts on 2,360 children with bruising. The proposed study will address the following specific aims: 1) Identify discriminating bruising characteristics utilizing a detailed prospective skin assessment approach to allow for model input and development 2) Determine the predictive accuracy of our existing BCDR to discriminate bruising caused by abusive vs. accidental trauma when applied prospectively in different clinical settings, and 3) Determine if the predictive accuracy of the existing BCDR can be improved upon with the additional dataset collected prospectively, or generate a new BCDR should the existing model prove inadequate. CDR modeling will be performed using a binary recursive partitioning algorithm. Success of this study will result in a BCDR which can be used as a screening tool to identify children and infants with bruising who are at high risk for physical abuse and require further evaluation. Our long term goal is to change practice through evidence-based guidelines in order to decrease the number of unrecognized cases of physical child abuse, thereby preventing further abuse, improving patient outcomes, and decreasing the large burden to society.